The answer is AWS WAF with an IP set rule that blocks the malicious IPs. This is correct because AWS WAF allows you to create IP set rules that explicitly deny traffic from specified source addresses, and when attached to an Application Load Balancer, it inspects every incoming request before it reaches the application. For the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of the appropriate layer for IP-based blocking versus other security controls—a common trap is confusing AWS WAF with Shield Advanced, which provides DDoS mitigation but not granular IP blocking, or with Network ACLs, which are stateless and require cumbersome bidirectional rules. Remember that WAF operates at Layer 7 and is the only service designed for application-level allow/deny lists against an ALB. A useful memory tip: “WAF blocks the bad actors at the door, while Shield stops the flood.”
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company has deployed a web application behind an Application Load Balancer (ALB) in a VPC. The security team wants to block a list of known malicious IP addresses from accessing the application. Which service should they use to implement this protection?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AWS WAF with an IP set rule that blocks the malicious IPs
Option A is correct because AWS WAF with IP set rules can block malicious IPs. Option B is wrong because Shield Advanced provides DDoS protection, not IP blocking. Option C is wrong because Network ACLs are stateless and less efficient for this use case. Option D is wrong because Security Groups are stateful but not designed for IP blocking at the ALB level.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Network ACLs on the ALB subnet with deny rules
Why it's wrong here
Network ACLs are stateless and affect all traffic, not targeted.
✓
AWS WAF with an IP set rule that blocks the malicious IPs
Shield Advanced is for DDoS mitigation, not custom IP blocking.
✗
Security Groups for the ALB with deny rules
Why it's wrong here
Security groups support allow rules only, not deny.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: AWS WAF with an IP set rule that blocks the malicious IPs — Option A is correct because AWS WAF with IP set rules can block malicious IPs. Option B is wrong because Shield Advanced provides DDoS protection, not IP blocking. Option C is wrong because Network ACLs are stateless and less efficient for this use case. Option D is wrong because Security Groups are stateful but not designed for IP blocking at the ALB level.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses AWS WAF to protect a web application behind an Application Load Balancer. The security team notices that a specific IP address is generating a high number of requests and wants to block it immediately. What is the MOST efficient way to block this IP address?
medium
✓ A.Add the IP address to an IP set in AWS WAF and update the rule to block it
B.Add a deny rule in the security group attached to the ALB
C.Update the Network ACL associated with the ALB subnets to deny inbound traffic from the IP address
D.Create a new web ACL in AWS WAF and associate it with the ALB
Why A: Option C is correct because AWS WAF allows creating an IP set and updating a rule to block it, providing immediate effect. Option A is wrong because a Network ACL can block IPs at the subnet level but requires updating the NACL, which is less granular and slower. Option B is wrong because security groups cannot block specific IPs in inbound rules for ALB traffic; they work at the instance level. Option D is wrong because creating a new web ACL and associating it takes more steps than updating an existing rule.
Variation 2. A company is using AWS WAF to protect a web application behind an Application Load Balancer. They want to block requests from a specific IP address range. Which component should they use?
easy
A.Security group associated with the ALB
✓ B.IP set match condition in AWS WAF
C.AWS Shield Advanced
D.Network ACL on the ALB's subnets
Why B: Option C is correct because AWS WAF has IP set match conditions that allow you to specify IP addresses to block or allow. Option A is wrong because security groups are stateful firewalls for EC2 instances, not for ALB. Option B is wrong because NACLs are stateless firewalls at the subnet level, not integrated with ALB. Option D is wrong because AWS Shield Advanced is for DDoS protection, not IP-based blocking.
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.